Fix typo in tutorial
Fix typo in tutorial

wkentaro/chainer,keisuke-umezawa/chainer,okuta/chainer,ktnyt/chainer,ronekko/chainer,pfnet/chainer,rezoo/chainer,niboshi/chainer,keisuke-umezawa/chainer,ktnyt/chainer,wkentaro/chainer,wkentaro/chainer,jnishi/chainer,hvy/chainer,okuta/chainer,chainer/chainer,niboshi/chainer,jnishi/chainer,jnishi/chainer,kiyukuta/chainer,chainer/chainer,ktnyt/chainer,chainer/chainer,kashif/chainer,aonotas/chainer,keisuke-umezawa/chainer,anaruse/chainer,delta2323/chainer,okuta/chainer,chainer/chainer,jnishi/chainer,niboshi/chainer,hvy/chainer,ktnyt/chainer,niboshi/chainer,tkerola/chainer,ysekky/chainer,hvy/chainer,hvy/chainer,keisuke-umezawa/chainer,okuta/chainer,wkentaro/chainer